1. Field of the Invention
The present invention relates to a rotary microactuator integrating optimally curved electrodes.
2. Description of the Related Art
FIGS. 1 and 2 illustrate the driving principle of conventional linear microactuators. A linear microactuator of a type shown in FIG. 1 has a structure in which a stator 10 and a rotor 20 are aligned at regular intervals g0. On the other hand, a linear microactuator of a type shown in FIG. 2 has a stator 30 and a rotor 40 which are tilted by xcex8t from a direction perpendicular to the driving direction in a transverse mode. The electrode structure of this type of microactuator is disclosed in Electronics Letters, 1998, Vol. 34, No. 18, pp 1787-1788.
FIG. 3 is a view for illustrating the basic operating principle of a rotatory microactuator. The driving method of a rotary electrostatic microactuator includes methods of two types: an interdigited configuration (another name is a comb-type) type; and a parallel-plate configuration electrode type. A force generated in the case of the interdigited configuration type is inversely proportional to the interval between two electrodes, but a force generated in the case of the parallel-plate configuration electrode type is inversely proportional to the square of the interval between two electrodes. Thus, as the interval between electrodes becomes narrower, the parallel-plate configuration electrode type has a greater driving force than the driving force of the interdigited configuration type. Due to the continuous development of new process techniques, the interval between two electrodes is being reduced. Hence, in the future, it is estimated that the merits of parallel-plate electrode type rotary electrostatic microactuators will be more highlighted. In order to meet this trend, techniques of maximizing the driving force of the conventional parallel-plate electrode by focusing on the parallel-plate electrode must be developed.
A rotary microactuator using such a parallel-plate electrode is actually disclosed in Journal Microelectromechanical systems, pp 141-148, Vol. 7, No. 2, June 1998. As shown in FIG. 3, a conventional rotary microactuator has a structure in which two parallel-plate configuration electrodes, that is, a stator 100 and a rotor 200, are aligned perpendicularly to the direction of driving (rotation). In this rotary microactuator, the gap between the electrodes becomes wider in the direction of the outside. Since the driving distance is proportional to the radius, the interval between two electrodes must be increased in the direction toward the outside. Also, when a large displacement is required, the interval between electrodes in initial state before a voltage is applied must be wide, so that the interval between electrodes must be wide. Therefore, the merit of a parallel-plate electrode in that a large driving force can be generated when the gap between electrodes is narrow, is not sufficiently employed.
To solve the above problem, an objective of the present invention is to provide a rotary microactuator by which parallel-plate configuration electrodes can generate a maximum driving force by designing electrodes so that the vertical interval between electrodes is uniformly maintained to a minimum interval that can be obtained during the electrode manufacturing process regardless of an arbitrary radius of an electrode between the inner radius and the outer radius.
To achieve the above objective, the present invention provides a rotary microactuator having a rotor and a stator optimally-shaped plate electrodes for driving rotation, wherein the rotor and the stator have a tangent tilting angle which continuously varies according to a radius from the central axis of the rotor so that the interval between the rotor and the stator in the normal direction to the curvature of the rotor and stator is constant regardless of a radius from the central axis of the rotor, in order to generate a maximum rotation driving force.
Preferably, the tangent tilting angle xcex8t(r,gf) depending on the radius r is expressed as in the following Equation:                     θ        t            ⁡              (                  r          ,                      g            f                          )              =                  cos                  -          1                    ⁡              (                              g            f                                nr            ⁢                          xe2x80x83                        ⁢                          θ              0                                      )              ,
when in the manufacture of the rotor and the stator, the minimum interval between the two electrodes that can be obtained by a process is set to be gf, a driving angle required by the actuator is set to be xcex80, a factor for satisfying the static stability of the two electrodes within an electrical field is set to be n, and the radius is set to be r. It is also preferable that an electrode position angle xcex8e(r*) formed by the axis of an electrode position radius r* from the axis of the inner radius r1 at which an electrode begins is expressed as in the following Equation:             θ      e        ⁡          (              r        *            )        =            ∫      r1              r        *              ⁢                            tan          ⁡                      (                                          cos                                  -                  1                                            ⁡                              (                                                      g                    f                                                        r                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      0                                                                      )                                      )                          r            ⁢              ⅆ        r            
wherein n denotes a factor for satisfying the static stability of the two electrodes within an electrical field, r1 denotes the inner radius of the rotor, which is the distance to the innermost portions of the two electrodes, r2 denotes the outer radius of the rotor, which is the distance to the outermost portions of the two electrodes, xcex80 denotes a driving angle required by the actuator between the inner radius and the outer radius, and r* denotes an electrode position radius from the central axis of the rotor to an arbitrary point on each of the two electrodes within the required driving angle xcex80.
To achieve the above objective, the present invention provides another type of a rotary microactuator including a rotor and a stator as optimally-shaped plate electrodes for driving rotation, wherein the rotor and the stator have a zigzag shape so that the interval between the rotor and the stator in the normal direction is constant regardless of a distance from the central axis of the rotor, in order to generate the same maximum rotation driving force as that of the firstly-introduced rotary microactuator.
In the rotary microactuator, preferably, the rotor and the stator are zigzagged more sharply in the direction of the outer radius of the rotor, so that the width of each piece in the circumferential direction is constant. However, it is preferable that each zigzagged piece of the rotor and the stator has a continuous tilting angle along the radius from the central axis of the rotor. In order to achieve this, the tangent tilting angle xcex8t(r,gf) with respect to the axis of the radius r is expressed as in the following Equation:                     θ        t            ⁡              (                  r          ,                      g            f                          )              =                  cos                  -          1                    ⁡              (                              g            f                                nr            ⁢                          xe2x80x83                        ⁢                          θ              0                                      )              ,
when in the manufacture of pieces from the zigzagged rotor and the zigzagged stator, the minimum interval between the two electrodes that can be obtained by a process is set to be gf, a driving angle required by the actuator is set to be xcex80, a factor for satisfying the static stability of the two electrodes within an electrical field is set to be n, and the radius is set to be r. The zigzag shape switches the tilting direction alternatively, one for clockwise and the other for counterclockwise while the magnitude of the tilting angle adopts the one given by Equation:             θ      t        ⁡          (              r        ,                  g          f                    )        =                    cos                  -          1                    ⁡              (                              g            f                                nr            ⁢                          xe2x80x83                        ⁢                          θ              0                                      )              .  